DOCSLIB.ORG

Determining the Origin of the Monoceros Tidal Stream

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Determining the Origin of the Monoceros Tidal Stream DETERMINING THE ORIGIN OF THE MONOCEROS RING Chloe Keeling University of Tennessee HEP Seminar April 19 2017 OUTLINE • Morphology of the Milky Way • Explanations for Monoceros Tidal Stream • Tidal Stream • Flared Thick Disk • Disrupted Disk • Conclusion GALACTIC COORDINATES Galactic Longitude: l Galactic Latittude: b Auger.org STRUCTURE OF THE MILKY WAY Velocity Dispersions: Thin: 15-25 km/s Thick: ~45 km/s Halo: ~100 km/s Swinburne University BASIC PROPERTIES OF THE MONOCEROS RING • Over density of stars in the region of 100° < < 230° and 30° < < 35° • ~25 kpc from galactic center − • [Fe/H]= 0.95 ± 0.15 • Co-rotating with the disk • Scale Height: ~3.5 kpc • Velocity Dispersion: ~25 km/s • Stellar Mass in all of Monoceros: 107-108 M 7 • Observable Stellar Mass : 3x10 M ⊙ ⊙ POSSIBLE EXPLANATIONS FOR THE MONOCEROS RING • 1. Tidal Stream • 2. Flared and warped thick disk • 3. Disrupted thin disk (north/south stellar density asymmetry) EVIDENCE FOR TIDAL OR HALO ORIGIN • Presence of RR Lyrae variable stars (Mateu et al. 2012) • Globular clusters with orbits that match Monoceros (Frenchaboy 2006) • Non-zero radial velocity at l=180 • Canis Major: Dwarf Galaxy located∘ at (l,b)=(240 , -8 ) • Model by Peñarrubia et al. 2005 produced correct∘ b ∘values and velocities with 10-20 km/s of observation • We aren’t sure this is actually a dwarf galaxy is could be an outer spiral arm that is observable at the (l, b) values because of the galactic warp HR DIAGRAM EVIDENCE CONTRARY TO TIDAL OR HALO ORIGIN • Presence of M giants (Indicative of Metal Rich origin) • Present at low galactic latitude • Nearly circular prograde orbit (models of tidal streaming events have had significant difficulty matching) • Same model by Peñarrubia et al. 2005 has problems filling in the band like structure observed FLARED DISK EVIDENCE FOR A FLARED THICK DISK • Present at low galactic latitude • Nearly circular prograde orbit • Presence of M giants (Indicative of Metal Rich origin) • Canis Major can be explained by a warped disk + spiral arm EVIDENCE CONTRARY TO FLARED THICK DISK • Evidence for small scale height of the thick disk ~1.8 kpc (Cheng et al. 2012) • Presence of RR Lyrae variable stars • North-South stellar density assymetry DISRUPTED DISK HESS DIAGRAM WHAT DID I DO ABOUT IT? Metallic Line A type Stars: Chemically peculiar spectral lines This is caused by gravitational settling and radiative levitation of the various elements in the quiescent atmosphere of non- convective, slowly rotating A- stars OBJECTIVE • Determine the frequency with which A type stars present with peculiar spectral lines in globular clusters, in the thick disk, and in Monoceros Ring • Characterize the A type stars • Determine proper motions • [Fe/H] • [α/H] SAMPLE OF FIELD STARS • 5865 blue stragglers and 670 blue stragglers displaying the Am effect • bias to stars that are more metal rich and have high signal-to-noise ratios • Determine Metallicty • -1.1<[Fe/H]<-0.5 • Found using kinematics and known iron deficiency of other Am stars WHERE TO NOW? • Further study of relevant globular clusters and halo stars. • Further study and characterization of the Monoceros ring stellar population • Further study and characterization of the thin and thick disk populations near Monoceros REFERENCES • “Tidal Streams in the Local Group and Beyond: Observations and Implications” by Heidi Jo Newberg and Jeffery L Carlin (2015) .
Load more

Recommended publications
  • Spatial and Kinematic Structure of Monoceros Star-Forming Region
    MNRAS 476, 3160–3168 (2018) doi:10.1093/mnras/sty447 Advance Access publication 2018 February 22 Spatial and kinematic structure of Monoceros star-forming region M. T. Costado1‹ and E. J. Alfaro2 1Departamento de Didactica,´ Universidad de Cadiz,´ E-11519 Puerto Real, Cadiz,´ Spain. Downloaded from https://academic.oup.com/mnras/article-abstract/476/3/3160/4898067 by Universidad de Granada - Biblioteca user on 13 April 2020 2Instituto de Astrof´ısica de Andaluc´ıa, CSIC, Apdo 3004, E-18080 Granada, Spain Accepted 2018 February 9. Received 2018 February 8; in original form 2017 December 14 ABSTRACT The principal aim of this work is to study the velocity field in the Monoceros star-forming region using the radial velocity data available in the literature, as well as astrometric data from the Gaia first release. This region is a large star-forming complex formed by two associations named Monoceros OB1 and OB2. We have collected radial velocity data for more than 400 stars in the area of 8 × 12 deg2 and distance for more than 200 objects. We apply a clustering analysis in the subspace of the phase space formed by angular coordinates and radial velocity or distance data using the Spectrum of Kinematic Grouping methodology. We found four and three spatial groupings in radial velocity and distance variables, respectively, corresponding to the Local arm, the central clusters forming the associations and the Perseus arm, respectively. Key words: techniques: radial velocities – astronomical data bases: miscellaneous – parallaxes – stars: formation – stars: kinematics and dynamics – open clusters and associations: general. Hoogerwerf & De Bruijne 1999;Lee&Chen2005; Lombardi, 1 INTRODUCTION Alves & Lada 2011).
    [Show full text]
  • Nd AAS Meeting Abstracts
    nd AAS Meeting Abstracts 101 – Kavli Foundation Lectureship: The Outreach Kepler Mission: Exoplanets and Astrophysics Search for Habitable Worlds 200 – SPD Harvey Prize Lecture: Modeling 301 – Bridging Laboratory and Astrophysics: 102 – Bridging Laboratory and Astrophysics: Solar Eruptions: Where Do We Stand? Planetary Atoms 201 – Astronomy Education & Public 302 – Extrasolar Planets & Tools 103 – Cosmology and Associated Topics Outreach 303 – Outer Limits of the Milky Way III: 104 – University of Arizona Astronomy Club 202 – Bridging Laboratory and Astrophysics: Mapping Galactic Structure in Stars and Dust 105 – WIYN Observatory - Building on the Dust and Ices 304 – Stars, Cool Dwarfs, and Brown Dwarfs Past, Looking to the Future: Groundbreaking 203 – Outer Limits of the Milky Way I: 305 – Recent Advances in Our Understanding Science and Education Overview and Theories of Galactic Structure of Star Formation 106 – SPD Hale Prize Lecture: Twisting and 204 – WIYN Observatory - Building on the 308 – Bridging Laboratory and Astrophysics: Writhing with George Ellery Hale Past, Looking to the Future: Partnerships Nuclear 108 – Astronomy Education: Where Are We 205 – The Atacama Large 309 – Galaxies and AGN II Now and Where Are We Going? Millimeter/submillimeter Array: A New 310 – Young Stellar Objects, Star Formation 109 – Bridging Laboratory and Astrophysics: Window on the Universe and Star Clusters Molecules 208 – Galaxies and AGN I 311 – Curiosity on Mars: The Latest Results 110 – Interstellar Medium, Dust, Etc. 209 – Supernovae and Neutron
    [Show full text]
  • Cresting the Wave: Proper Motions of the Eastern Banded Structure
    MNRAS 000,1{6 (2017) Preprint 28th June 2018 Compiled using MNRAS LATEX style file v3.0 Cresting the wave: Proper motions of the Eastern Banded Structure Alis J. Deason1?, Vasily Belokurov2, Sergey E. Koposov2;3, 1Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK 2Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 3McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA Accepted XXX. Received YYY; in original form ZZZ ABSTRACT We study the kinematic properties of the Eastern Banded Structure (EBS) and Hydra I overdensity using exquisite proper motions derived from the Sloan Digital Sky Survey (SDSS) and Gaia source catalog. Main sequence turn-off stars in the vicinity of the EBS are identified from SDSS photometry; we use the proper motions and, where applicable, spectroscopic measurements of these stars to probe the kinematics of this apparent stream. We find that the EBS and Hydra I share common kinematic and chemical properties with the nearby Monoceros Ring. In particular, the proper motions of the EBS, like Monoceros, are indicative of prograde rotation (Vφ ∼ 180 − 220 km s−1), which is similar to the Galactic thick disc. The kinematic structure of stars in the vicinity of the EBS suggest that it is not a distinct stellar stream, but rather marks the \edge" of the Monoceros Ring. The EBS and Hydra I are the latest substructures to be linked with Monoceros, leaving the Galactic anti-centre a mess of interlinked overdensities which likely share a unified, Galactic disc origin.
    [Show full text]
  • Arxiv:1801.01171V1 [Astro-Ph.GA] 3 Jan 2018
    Draft version November 5, 2018 Typeset using LATEX twocolumn style in AASTeX61 A DISK ORIGIN FOR THE MONOCEROS RING AND A13 STELLAR OVERDENSITIES Allyson A. Sheffield,1 Adrian M. Price-Whelan,2 Anastasios Tzanidakis,3 Kathryn V. Johnston,3 Chervin F. P. Laporte,3 and Branimir Sesar4 1Department of Natural Science, City University of New York, LaGuardia Community College, Long Island City, NY 11101, USA 2Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA 3Department of Astronomy, Columbia University, Mail Code 5246, New York, NY 10027, USA 4Max Planck Institute for Astronomy, K¨oenigstuhl17, 69117, Heidelberg, Germany ABSTRACT The Monoceros Ring (also known as the Galactic Anticenter Stellar Structure) and A13 are stellar overdensities at estimated heliocentric distances of d ∼ 11 kpc and 15 kpc observed at low Galactic latitudes towards the anticenter of our Galaxy. While these overdensities were initially thought to be remnants of a tidally-disrupted satellite galaxy, an alternate scenario is that they are composed of stars from the Milky Way (MW) disk kicked out to their current location due to interactions between a satellite galaxy and the disk. To test this scenario, we study the stellar populations of the Monoceros Ring and A13 by measuring the number of RR Lyrae and M giant stars associated with these overdensities. We obtain low-resolution spectroscopy for RR Lyrae stars in the two structures and measure radial velocities to compare with previously measured velocities for M giant stars in the regions of the Monoceros Ring and A13, to assess the fraction of RR Lyrae to M giant stars (fRR:MG) in A13 and Mon/GASS.
    [Show full text]
  • The Edge of the Young Galactic Disk
    The Astrophysical Journal, 718:683–694, 2010 August 1 doi:10.1088/0004-637X/718/2/683 C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. THE EDGE OF THE YOUNG GALACTIC DISK Giovanni Carraro1,6, Ruben A. Vazquez´ 2, Edgardo Costa3, Gabriel Perren4,7,andAndre´ Moitinho5 1 ESO, Alonso de Cordova 3107, 19100 Santiago de Chile, Chile 2 Facultad de Ciencias Astronomicas´ y Geof´ısicas (UNLP), Instituto de Astrof´ısica de La Plata (CONICET, UNLP), Paseo del Bosque s/n, La Plata, Argentina 3 Departamento de Astronom´ıa, Universidad de Chile, Casilla 36-D, Santiago, Chile 4 Instituto de F´ısica de Rosario, IFIR (CONICET-UNR), Parque Urquiza, 2000 Rosario, Argentina 5 SIM/IDL, Faculdade de Ciencias´ da Universidade de Lisboa, Ed. C8, Campo Grande, 1749-016 Lisboa, Portugal Received 2009 August 17; accepted 2010 June 2; published 2010 July 6 ABSTRACT In this work, we report and discuss the detection of two distant diffuse stellar groups in the third Galactic quadrant. They are composed of young stars, with spectral types ranging from late O to late B, and lie at galactocentric distances between 15 and 20 kpc. These groups are located in the area of two cataloged open clusters (VdB–Hagen 04 and Ruprecht 30), projected toward the Vela-Puppis constellations, and within the core of the Canis Major overdensity. Their reddening and distances have been estimated by analyzing their color–color and color–magnitude diagrams, derived from deep UBV photometry. The existence of young star aggregates at such extreme distances from the Galactic center challenges the commonly accepted scenario in which the Galactic disk has a sharp cutoff at about 14 kpc from the Galactic center and indicates that it extends to much greater distances (as also supported by the recent detection of CO molecular complexes well beyond this distance).
    [Show full text]
  • Print This Press Release
    PRESS RELEASE Released on March 16th, 2006 Deriving the shape of the Galactic stellar disc Based on the article “Outer structure of the Galactic warp and flare: explaining the Canis Major over- density”, by Momany et al. To be published in Astronomy & Astrophysics. This press release is issued as a collaboration with the Italian Institute for Astrophysics (INAF) and Astronomy & Astrophysics. While analysing the complex structure of the Milky Way, an international team of astronomers from Italy and the United Kingdom has recently derived the shape of the Galactic outer stellar disc, and provided the strongest evidence that, besides being warped, it is at least 70% more extended than previously thought. Their findings will be reported in an upcoming issue of Astronomy & Astrophysics, and is a new step in understanding the large-scale structure of our Galaxy. Using the 2MASS all-sky near infrared catalogue, Yazan Momany and his collaborators reconstructed the outer structure of the Galactic stellar disc, in particular, its warp. Their work will soon be published in Astronomy & Astrophysics. Observationally, the warp is a bending of the Galactic plane upwards in the first and second Galactic longitude quadrants (0<l<180 degrees) and downwards in the third and fourth quadrants (180<l<360 degrees). Although the origin of the warp remains unknown, this feature is seen to be a ubiquitous property of all spiral galaxies. As we are located inside the Galactic disc, it is difficult to unveil specific details of its shape. To appreciate a warped stellar disc one should, therefore, look at other galaxies. Figure 1 shows a good example of what a warped galaxy looks like.
    [Show full text]
  • Stellar Streams Discovered in the Dark Energy Survey
    Draft version January 9, 2018 Typeset using LATEX twocolumn style in AASTeX61 STELLAR STREAMS DISCOVERED IN THE DARK ENERGY SURVEY N. Shipp,1, 2 A. Drlica-Wagner,3 E. Balbinot,4 P. Ferguson,5 D. Erkal,4, 6 T. S. Li,3 K. Bechtol,7 V. Belokurov,6 B. Buncher,3 D. Carollo,8, 9 M. Carrasco Kind,10, 11 K. Kuehn,12 J. L. Marshall,5 A. B. Pace,5 E. S. Rykoff,13, 14 I. Sevilla-Noarbe,15 E. Sheldon,16 L. Strigari,5 A. K. Vivas,17 B. Yanny,3 A. Zenteno,17 T. M. C. Abbott,17 F. B. Abdalla,18, 19 S. Allam,3 S. Avila,20, 21 E. Bertin,22, 23 D. Brooks,18 D. L. Burke,13, 14 J. Carretero,24 F. J. Castander,25, 26 R. Cawthon,1 M. Crocce,25, 26 C. E. Cunha,13 C. B. D'Andrea,27 L. N. da Costa,28, 29 C. Davis,13 J. De Vicente,15 S. Desai,30 H. T. Diehl,3 P. Doel,18 A. E. Evrard,31, 32 B. Flaugher,3 P. Fosalba,25, 26 J. Frieman,3, 1 J. Garc´ıa-Bellido,21 E. Gaztanaga,25, 26 D. W. Gerdes,31, 32 D. Gruen,13, 14 R. A. Gruendl,10, 11 J. Gschwend,28, 29 G. Gutierrez,3 B. Hoyle,33, 34 D. J. James,35 M. D. Johnson,11 E. Krause,36, 37 N. Kuropatkin,3 O. Lahav,18 H. Lin,3 M. A. G. Maia,28, 29 M. March,27 P. Martini,38, 39 F. Menanteau,10, 11 C.
    [Show full text]
  • The Monoceros Ring: the Evidence and Possible Solutions
    The Monoceros Ring: the evidence and possible solutions Blair Conn ESO Fellow ESO Chile 2009 Who am I? – Blair Conn •PhD from •The University of Sydney, 2006 •ESO Fellow •2p2/Wide Field Imager Instrument Scientist •[email protected] ESO Chile 2009 Discovery of the Monoceros Ring in SDSS data Newberg et al, 2002 ESO Chile 2009 Discovery of the Monoceros Ring in SDSS data Newberg et al, 2002 ESO Chile 2009 Searching for the Monoceros Ring ESO Chile 2009 Surveying the Monoceros Ring INT/WFC SUBARU/SUPRIMECAM AAT/WFI ESO Chile 2009 So Surveyingwhat did we the find Monoceros.... ? Ring INT/WFC 14 detections SUBARU/SUPRIMECAM +3 maybes AAT/WFI ESO Chile 2009 Using Radial Velocities Distance Distance Velocity Heliocentric Galactocentric AAT/2dF ESO Chile 2009 Properties of the Monoceros Ring • Dense grouping of stars at a specific distance • Large extent on the sky • Narrow velocity dispersion ESO Chile 2009 What are the options for the Monoceros Ring? ESO Chile 2009 What are the options for the Monoceros Ring? Known Galactic Structure Messy left over Galaxy formation fluff ESO Chile 2009 What are the options for the Monoceros Ring? Known Galactic Structure Messy left over Galaxy formation fluff Warp Flare Dwarf Galaxy Disrupted Disc Tidal Stream From infalling dSph Spiral Arm ESO Chile 2009 Warp Let's take an extreme example UGC 3697 ESO Chile 2009 Warp The argument goes that the Canis Major overdensity, the purported progenitor of the Monoceros Ring is simply the shifted midplane of the Galaxy. UGC 3697 ESO Chile 2009 Warp The argument goes that the Canis Major overdensity, the purported progenitor of the Monoceros Ring is simply the shifted midplane of the Galaxy.
    [Show full text]
  • A Population of Halo Stars Kicked out of the Galactic Disk
    City University of New York (CUNY) CUNY Academic Works Publications and Research LaGuardia Community College 2015 A re-interpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disk Adrian M. Price-Whelan Columbia University Kathryn V. Johnston Columbia University Allyson A. Sheffield CUNY La Guardia Community College Chervin F. P. Laporte Columbia University Branimir Sesar Max-Planck-Institut für Astronomie How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/lg_pubs/65 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] A re-interpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disk Adrian M. Price-Whelan1, Kathryn V. Johnston1, Allyson A. Sheffield2, Chervin F. P. Laporte1, Branimir Sesar3 ABSTRACT The Triangulum-Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of concentric ring- or shell-like over-densities at large R ( 30 kpc) and Z ( ≈ ≈ -10 kpc) in the Galactic halo that are thought to have been formed from the accretion and disruption of a satellite galaxy. This paper critically re-examines this formation scenario by comparing the number ratio of RR Lyrae to M giant stars associated with the TriAnd clouds with other structures in the Galaxy. The current data suggest a stellar population for these over-densities (fRR:MG < 0:38 at 95% confidence) quite unlike any of the known satellites of the Milky Way (fRR:MG 0:5 for the very largest and fRR:MG >> 1 for the smaller satellites) and ≈ more like the population of stars born in the much deeper potential well inhabited by the Galactic disk (fRR:MG < 0:01).
    [Show full text]
  • A Megacam Survey of Outer Halo Satellites. IV. Two Foreground
    DRAFT VERSION OCTOBER 21, 2018 Preprint typeset using LATEX style emulateapj v. 5/2/11 A MEGACAM SURVEY OF OUTER HALO SATELLITES. IV. TWO FOREGROUND POPULATIONS POSSIBLY ASSOCIATED WITH THE MONOCEROS SUBSTRUCTURE IN THE DIRECTION OF NGC 2419 AND KOPOSOV 21 JULIO A. CARBALLO-BELLO2 ,RICARDO R. MUÑOZ 2 ,JEFFREY L. CARLIN 3 ,PATRICK CÔTÉ4 ,MARLA GEHA5 ,JOSHUA D. SIMON6 , S. G. DJORGOVSKI7 Draft version October 21, 2018 ABSTRACT The origin of the Galactic halo stellar structure known as the Monoceros ring is still under debate. In this work, we study that halo substructure using deep CFHT wide-field photometry obtained for the globular clusters NGC 2419 and Koposov 2, where the presence of Monoceros becomes significant because of their coincident projected position. Using Sloan Digital Sky Survey photometry and spectroscopy in the area surrounding these globulars and beyond, where the same Monoceros population is detected, we conclude that a second feature, not likely to be associated with Milky Way disk stars along the line-of-sight, is present as foreground population. Our analysis suggests that the Monoceros ring might be composed of an old stellar population of age t ∼ 9 Gyr and a new component ∼ 4 Gyr younger at the same heliocentric distance. Alternatively, this detection might be associated with a second wrap of Monoceros in that direction of the sky and also indicate a metallicity spread in the ring. The detection of such a low-density feature in other sections of this halo substructure will shed light on its nature. Subject headings: Galaxy: structure, halo, globular clusters: general 1.
    [Show full text]
  • Arxiv:1907.10678V1 [Astro-Ph.GA] 24 Jul 2019 1 INTRODUCTION Tributaries of the Galactic Anticenter, We Count the Mono- Ceros Ring (Newberg Et Al
    Mon. Not. R. Astron. Soc. 000, 1{6 (2018) Printed 26 July 2019 (MN LATEX style file v2.2) Chemo-dynamical properties of the Anticenter Stream: a surviving disc fossil from a past satellite interaction. Chervin F. P. Laporte1?y, Vasily Belokurov2, Sergey E. Koposov3;2, Martin C. Smith4,Vanessa Hill5 1Department of Physics & Astronomy, University of Victoria, 3800 Finnerty Road, Victoria BC, Canada V8P 5C2 2Institute of Astronomy, University of Cambridge, Madingley road, CB3 0HA, UK 3McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave, 15213, USA 4Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China 5Laboratoire Lagrange, Universit´eC^otedAzur, Observatoire de la C^otedAzur, Boulevard de lObservatoire, CS 34229, 06304, Nice, France Accepted . Received ; in original form ABSTRACT Using Gaia DR2, we trace the Anticenter Stream (ACS) in various stellar popula- tions across the sky and find that it is kinematically and spatially decoupled from the Monoceros Ring. Using stars from lamost and segue, we show that the ACS is sys- tematically more metal-poor than Monoceros by 0:1 dex with indications of a narrower metallicity spread. Furthermore, the ACS is predominantly populated of old stars (∼ 10 Gyr), whereas Monoceros has a pronounced tail of younger stars (6 − 10 Gyr) as revealed by their cumulative age distributions. Put togehter, all of this evidence support predictions from simulations of the interaction of the Sagittarius dwarf with the Milky Way, which argue that the Anticenter Stream (ACS) is the remains of a tidal tail of the Galaxy excited during Sgr's first pericentric passage after it crossed the virial radius, whereas Monoceros consists of the composite stellar populations ex- cited during the more extended phases of the interaction.
    [Show full text]
  • Introduction to Tidal Streams
    Introduction to Tidal Streams Heidi Jo Newberg Abstract Dwarf galaxies that come too close to larger galaxies suffer tidal disrup- tion; the differential gravitational force between one side of the galaxy and the other serves to rip the stars from the dwarf galaxy so that they instead orbit the larger galaxy. This process produces “tidal streams” of stars, which can be found in the stellar halo of the Milky Way, as well as in halos of other galaxies. This chapter provides a general introduction to tidal streams, including the mechanism through which the streams are created, the history of how they were discovered, and the observational techniques by which they can be detected. In addition, their use in unraveling galaxy formation history and the distribution of dark matter in galaxies is discussed, as is the interaction between these dwarf galaxy satellites and the disk of the larger galaxy. 1 An Overview Tidal Streams and Halo Substructure The Milky Way is a large, spiral galaxy. It is composed of stars, gas, and dark mat- ter within its “halo,” which is the region within which the matter is graviationally bound. Like other similar galaxies in the Universe, the Milky Way is also orbited by gravitationally bound satellites that contain their own stars, gas, and/or dark matter. Globular clusters contain stars, but are generally free of gas and dark matter. There are 157 known globular clusters in the Milky Way (Harris, 2010). Dwarf galaxies contain stars, sometimes gas, and are generally thought to contain large amounts of dark matter (though the dark matter content of dwarf galaxies is debated).
    [Show full text]